The invention concerns a device for automatically injecting a dose of a medicinal product.
A number of injection devices exist at the present time enabling an inexperienced patient to self-administer a dose of a medicinal product without having to force the needle into himself or herself and actuate the piston of the syringe.
Such injection devices are in particular described in patents EP 516,473, U.S. Pat. No. 3,797,489, U.S. Pat. No. 3,712,301, WO 95/35126, FR 2,654,938, and EP 577 448.
At the present time, for obvious safety reasons, the tendency consists of producing injection devices such as that described in patent EP 516 473, for single use including a propulsion spring designed to inject the medicinal product, and a propulsion spring designed to push the syringe back automatically into the casing after injection. According to this design, the needle of the syringe only projects from the casing during the time of injection and no risk of injury with a soiled needle is therefore to be feared.
Although such injection devices provide an appreciable advantage as regards their safety of use, they however have several disadvantages. In point of fact, in the first place, on account of the manufacturing dimensional tolerances of the syringes, and of the presence of the return propulsion spring, it is virtually impossible to guarantee injection of all the dose enclosed in the said syringes. Now, for certain products such as heparin or specific vaccines, the dose of the product injected must be guaranteed in a very precise manner, a condition which current injection devices cannot systematically fulfill.
Moreover, most of the current injection devices offering this safety of use for the patient prove to have a complexity which leads to a cost price which is hardly compatible with that of a single-use device. Moreover, on account of their design, they generally require the use of specific syringes of which the cost price is out of all proportion with that of conventional syringes used without an automatic injection device.
These last two disadvantages have been overcome by the injection device described in patent application WO 94/21316 which comprises:
a long narrow casing having a front wall pierced by an orifice, and formed of two parts, a front part and a rear part, fitted one into the other and capable of sliding longitudinally in relation to each other over a short traverse so as to be able to undergo a relative movement between two positions: a retracted, so called rest position, of the rear part with respect to the front part obtained naturally in the absence of an external force exerted on the said parts, and a forward, so-called injection position, of the rear part with respect to the front part obtained by means of a longitudinal force exerted on the said rear part,
a syringe disposed in the casing and including a syringe body housing a piston, provided with a finger rest ring and carrying a needle,
a piston rod provided with a collar and extending into the rear extension of the syringe,
means for supporting the collar of the piston rod,
a propulsion spring extending between the means for supporting the collar of the piston rod and the bottom of the rear part of the casing,
means for locking in translation the means for supporting the collar of the piston rod capable of supporting them inside the casing in a position where the propulsion spring is compressed, and where the syringe is entirely housed inside the said casing, and capable of allowing their movement towards a forward position at the end of injection, produced by the propulsion spring, after the parts of the casing are moved from their retracted position to their forward position,
a device for stopping the syringe body in a forward position of the latter where the needle extends at least partially through the orifice of the casing,
means for triggering the means for supporting the collar of the piston rod capable of freeing the said collar, in the forward position of the said supporting means, after the parts of the casing are moved from their forward position to their retracted position,
and a return propulsion spring with a force less than that of the propulsion spring, disposed around the syringe body so as to be compressed by the finger rest ring of the said syringe body when the latter is moved to its forward position.
However, such an injection device does not enable the aforementioned first disadvantage to be overcome, namely to guarantee injection of the entire dose.
The present invention aims to overcome this disadvantage and its object is to provide an automatic injection device designed so as to enable a strictly defined dose of a medicinal product to be injected systematically.
Another object of the invention is to provide an injection device with a simplified design and therefore with a cost price compatible with that of a single-use device.
Another object of the invention is to provide an injection device which can be used with pre-filled syringes of the traditional type.
To this end, the invention concerns a device for automatically injecting a dose of a medicinal product of the type described in patent application WO 94/21316.
According to the invention, this injection device is characterized in that:
it includes means for viewing provided in the wall of the casing so as to enable the means for supporting the collar of the piston rod in their forward position to be seen,
means for supporting the collar of the piston rod comprising:
an inner, so called guide tube, extending into the rear part of the casing so as to delimit a peripheral annular space within the latter adapted so as to house the propulsion spring in the compressed position of the said spring,
a cage with a form adapted so as to slide inside the guide tube, and to house the piston rod and the collar thereof, the said cage including towards one of its ends, the so-called rear end, an internal device for locking the collar of the piston rod capable of deforming radially and, towards its other forward end, a front wall for stopping the propulsion spring and for contacting the means of locking in translation the said supporting means in the retracted position of the latter,
the said guide tube and cage being adapted so that, in the forward position of the supporting means, the device for locking the collar of the piston rod remains imprisoned in the guide tube in the forward relative position of the parts of the casing, and is freed in the retracted relative position of the said parts of the casing.
According to the invention, injection is carried out by applying first of all and in a conventional manner the forward end of the casing against the skin. A pressure exerted on the rear part of the casing then permits the triggering of the propulsion spring and therefore the injection of the product. At the end of this injection, the patient has a visual indication of the end of the traverse which informs him or her that the entire dose has been injected. He or she may then relax the pressure on the rear part of the casing, a relaxation which will enable is this rear part to retract and consequently allow the syringe to return into the casing under the action of the return propulsion spring.
Such an injection device which firstly includes a casing in two parts of which the relative movement enables the tolerances in variations in the lengths of the syringes to be absorbed and enables injection and subsequent return of the syringe inside the casing to be triggered, and secondly includes a visual indication of the end of injection, thus makes it possible to deliver systematically the entire product enclosed in the syringe and moreover constitutes a single-use device eliminating any risk of pricking before and after use.
In addition, absorption of the variation tolerances in the lengths of the syringes is obtained in a very simple manner by providing a sufficient margin concerning the length of the cage remaining imprisoned in the inner tube at the end of injection.
Moreover, the guide tube and the cage preferably have dimensions adapted so as to house the piston rod and the finger rest ring of the syringe body, the said cage including an internal device for stopping the finger rest ring of the syringe body in the retracted position of the said cage, and a front wall provided with an opening for permitting relative movement of this cage and the syringe body in the forward position of the latter.
The presence of this internal device for stopping the finger rest ring of the syringe body advantageously makes it possible to prevent the said syringe body from being entrained forwards when the protective end of the needle is withdrawn. Indeed, this entrainment, observed with current devices, and which tends to compress the return propulsion spring, results in difficulties for the user who, observing a resistance resulting from this compression, may hesitate to exert forces aimed at overcoming this resistance.
According to another characteristic of the invention, this injection device is adapted so as to be used with a traditional syringe of which the finger rest ring has a truncated annular form and includes two diametrically opposed flats. To this end, the cage consists of a stirrup having two longitudinal legs arranged so that each comes into contact with a flat of the finger rest ring.
Such a stirrup has the advantage of constituting an element for locking the syringe body in rotation, having a small overall transverse size, which combined with the arrangement of the propulsion spring in an annular space situated around the said stirrup, results in an injection device being obtained with a reduced overall size.
According to two preferred embodiments involving the stirrup:
the internal device for locking the collar of the piston rod consists of transverse grooves provided facing the legs of the stirrup,
this stirrup includes a ring in the rear extension of which the longitudinal legs extend, the internal device for stopping the finger rest ring of the syringe body including at least one inclined tongue extending longitudinally inside the said ring.
According to another characteristic of the invention:
the rear part of the casing has the form externally of a sleeve with a generally cylindrical form,
the front part of the casing has dimensions adapted so as to be housed over most of its length inside the rear part of the said casing,
guiding devices are adapted so as to enable the rear part of the casing to move over a short traverse along the front part of the said casing.
This arrangement of the front and rear parts of the casing makes it possible to obtain a casing which is perfectly rigid in flexion and which is therefore very safe in operation by the user.
According to another characteristic of the invention, the means for locking in translation the means for supporting the collar of the piston rod comprise:
a radially deformable stop device secured to the supporting means,
an internal axial device for stopping the deformable stop device, provided inside the rear part of the casing,
a trigger provided in the peripheral wall of the rear part of the casing so that it can deform and free the, device for stopping the supporting means, in the retracted position of the latter,
and an opening provided in the peripheral wall of the front part of the casing and with a form adapted firstly so that the stop devices extend through the said opening and secondly so as to enable the trigger to be actuated only in the forward relative position of the said, parts of the casing.
This arrangement makes it possible to provide a guarantee against any accidental triggering of the injection since the latter requires, first of all, a pressure to be exerted on the casing, and then secondly, a pressure to be applied to the trigger so as to retract the deformable device for stopping the supporting means.
According to a preferred embodiment, the trigger has a longitudinal T-shape, the opening having a corresponding shape and being provided so as to have a transverse arm offset longitudinally from the transverse bar of the trigger in the retracted relative position of the parts of the casing.
According to another characteristic of the invention, the injection device includes a cap with a form adapted so as to close off the front end section of the front part of the casing and to butt up against the rear part of the said causing in the retracted position of the latter.
Such a cap, apart from its conventional protective function, makes it possible to block the front and rear parts of the casing relatively in translation, before use, in the retracted position of the said parts.
In addition, the front part of the casing advantageously incorporates an internal conduit for guiding the syringe body extending over a portion of a length of the-said front part from the front wall of the latter, the said conduit having a shoulder for stopping the said syringe body in its forward position.
The cap also preferably includes claws extending longitudinally inside the said cap and disposed so as to lodge in the inner conduit for guiding the syringe body, the said claws being adapted so as to hook over an end piece protecting the needle of the syringe.
This arrangement makes it possible to withdraw automatically the end piece protecting the needle in a conventional manner, when the cap is removed.
In addition, according to another characteristic of the invention, the rear part of the casing and the cap have contact faces profiled in the shape of a cam so that the said cap can be removed by a rotational movement of the latter.